Fix required C standard from C90 to C99
Fix required C standard from C90 to C99

We are using C99 features, such as anonymous variadic macros and
mixed declarations and code.

Besides, we are using POSIX extensions (fork, etc.), so there is
(probably?) no point in forcing the use of the old ANSI C89 / ISO C90.

Signed-off-by: Mikko Johannes Koivunalho <b1070ee6d40473e0bf54e1be38982cfcedc3436a@iki.fi>

libcheck/check,libcheck/check,libcheck/check,libcheck/check,libcheck/check